<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body {
            color: white;
            background-color: #222;
        }

        .spot {
            position: absolute;
            width: 70px;
            height: 70px;
            border-radius: 35px;
            box-shadow: 0px 0px 40px #fff;
            background-color: #fff;
            opacity: .7;
        }
    </style>
</head>

<body>
    随着手指移动的小球
    <script>
        let spot = null;
        document.addEventListener("touchstart", (event) => {
            event.preventDefault();
            if (spot) {
                return;
            }
            spot = document.createElement('div');
            spot.classList.add('spot');
            spot.style.top = event.touches[0].pageX - 35 + "px";
            spot.style.left = event.touches[0].pageY - 35 + "px";
            document.body.appendChild(spot);
        }, false);
        document.addEventListener("touchmove", (event) => {
            event.preventDefault;
            if (spot) {
                spot.style.top = event.touches[0].pageY - 35 + "px";
                spot.style.left = event.touches[0].pageX - 35 + "px";
            }
        }, false);
        document.addEventListener("touchend", (event) => {
            event.preventDefault();
            if (spot) {
                document.body.removeChild(spot);
                spot = null;
            }
        }, false);
    </script>
</body>

</html>